This is a study of hyperactive children, their parents and siblings, and a group of normal control children, their parents and siblings. Part of the study is a long term follow up of hyperactive children maintained on stimulant medications. Hyperactive children will be studied with clinical, neurological, neurophysiological and psychological measures. There are several objectives of this study, as follows: (1) To ascertain the long term benefits and hazards of long term continuous stimulant medication. (2) To ascertain predictors of long term outcome. (3) To determine whether there is an increased prevalence of psychiatric illness (sociopathy, alcoholism, and hysteria) in the parents of hyperactive children. (4) To determine whether there is an increased prevalence of hyperactive child syndrome or learning disorders in the siblings of hyperactive children. (5) To determine if certain family relationships and characteristics (amount of warmth, quality of marital relationship, and type of parental discipline) are important in the development of antisocial behavior in the hyperactive child and his non-hyperactive sibling.